Syntheses and superoxide dismuting activities of partially (1-4) β-chlorinated derivatives of manganese(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin
Manganese(III) β-mono-, di-, tri-, and tetrachloro-5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnClx-TE-2-PyP5+, with x from 1 to 4) were prepared through β-chlorination of 5,10,15,20-tetrakis(2-pyridyl)porphyrin (H2T-2-PyP) followed by N-ethylation and metallation. Metal centered redox potentials and superoxide dismutation activities were measured. Starting from MnTE-2-PyP5+, whose redox potential and the related superoxide dismutation activity were E°1/2 = +228 mV vs NHE and kcat = 5.7 × 107 M-1 s-1, respectively, the average increase of 55 mV in the redox potential per added chlorine was accompanied by a 65% increase in the rate constant. With E°1/2 = +448 mV, the tetrachlorinated derivative MnCl4TE-2-PyP5+ exhibited the highest superoxide dismuting rate kcat = 4.0 × 108 M-1 s-1. The relationship between the redox properties (thermodynamic and kinetic factors) and the superoxide dismuting activity of such compounds is discussed. © 1999 American Chemical Society.
Kachadourian, R; Batinić-Haberle, I; Fridovich, I
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